self-defense. As noted by the authors, even small degrees of misreporting on ownership by either the cases or the controls can create substantial biases in the estimated risk factors (see Kleck, 1997, for an illustration of these biases). A more fundamental inferential problem arises from the fact that ownership is not likely to be random with respect to homicide or other forms of victimization. To the contrary, the decision to own a firearm may be directly related to the likelihood of being victimized. People may, for instance, acquire firearms in response to specific or perceived threats, and owners may be more or less psychologically prone toward violence. Thus, while the observed associations may reflect a causal albeit unspecified path-way, they may also be entirely spurious. As Kellermann and his colleagues note (1993:1089), “it is possible that reverse causation accounted for some of the association we observed between gun ownership and homicide.”

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